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United States Patent |
5,583,486
|
Kersten
|
December 10, 1996
|
Security access arrangement
Abstract
A three part security access arrangement in which the first part is
associated with an authorized person in the form of, for example a belt
buckle, the second part is attached to a valuable item, for example a
wallet, and the third part is associated with an area of restricted
access, such as a car. Access to the restricted area is denied unless all
three parts are in close proximity. If either of the first or second parts
are absent the third part will not allow access to the restricted area.
The first and second parts incorporate means for providing an audible
alarm if they are separated by greater than a pre-determined distance.
Inventors:
|
Kersten; Herbert (Adelaide, AU)
|
Assignee:
|
Monaad Corporation Pty Limited (Seacliff, AU)
|
Appl. No.:
|
347896 |
Filed:
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December 1, 1994 |
Foreign Application Priority Data
Current U.S. Class: |
340/572.1; 70/256; 180/287; 307/10.2; 340/5.62; 340/5.72; 340/426.16; 340/426.28; 340/426.36; 340/539.1; 340/539.23; 340/568.7; 455/100; 455/345 |
Intern'l Class: |
G08B 013/14 |
Field of Search: |
340/568,571,572,573,541,539,426
455/67.1,67.7,100,345
307/10.2,10.3,10.6
70/256,257
180/287
|
References Cited
U.S. Patent Documents
3478344 | Nov., 1969 | Schwitzgebel et al. | 340/539.
|
3891980 | Jun., 1975 | Lewis et al. | 340/572.
|
4260982 | Apr., 1981 | DeBenedictis et al. | 340/539.
|
4573046 | Feb., 1986 | Pinnow | 340/825.
|
4593273 | Jun., 1986 | Narcisse | 340/539.
|
4598272 | Jul., 1986 | Cox | 340/539.
|
4663625 | May., 1987 | Yewen | 340/825.
|
4733215 | Mar., 1988 | Memmola | 340/426.
|
4738334 | Apr., 1988 | Weishaupt | 340/426.
|
4785291 | Nov., 1988 | Hawthorne | 340/573.
|
4811013 | Mar., 1989 | Akutsu | 340/825.
|
4871997 | Oct., 1989 | Adriaenssens et al. | 340/539.
|
4899135 | Feb., 1990 | Ghahariiran | 340/573.
|
4942393 | Jul., 1990 | Waraksa et al. | 340/825.
|
4987406 | Jan., 1991 | Reid | 340/539.
|
5119072 | Jun., 1992 | Hemingway | 340/573.
|
5157389 | Oct., 1992 | Kurozu et al. | 307/10.
|
5196825 | Mar., 1993 | Young | 340/539.
|
5349329 | Sep., 1994 | Smith | 340/539.
|
Foreign Patent Documents |
87947/82 | Oct., 1982 | AU.
| |
17303/83 | Mar., 1984 | AU.
| |
68203/90 | Jun., 1991 | AU.
| |
2423015 | Dec., 1979 | FR | 340/426.
|
2543715 | Oct., 1984 | FR.
| |
3803541 | Aug., 1989 | DE.
| |
4003280 | Aug., 1991 | DE | 70/256.
|
4030880 | Apr., 1992 | DE | 307/10.
|
2233487 | Jan., 1991 | GB | 340/426.
|
2243476 | Oct., 1991 | GB.
| |
2259631 | Mar., 1993 | GB.
| |
84/03975 | Oct., 1984 | WO.
| |
87/06748 | Nov., 1987 | WO.
| |
9202911 | Feb., 1992 | WO | 70/256.
|
WO93/02897 | Feb., 1993 | WO.
| |
WO94/14639 | Jul., 1994 | WO.
| |
94/25944 | Nov., 1994 | WO.
| |
Other References
Derwent Abstract Accession No. 94-273647/34, GB 2276025 A (Barwell) 14 Sep.
1994.
Patent Abstracts of Japan, P1824, p. 67, JP 6-215281A (Toshinori Sekine) 5
Aug. 1994.
Patent Abstracts of Japan, P1179, p. 101, JP 3-1296A (Chou Electron
Services K.K.) 7 Jan. 1991.
Patent Abstracts of Japan, P857, p. 164, JP 63-316298A (NEC Corp.) 23 Dec.
1988.
|
Primary Examiner: Mullen; Thomas
Attorney, Agent or Firm: Merchant, Gould, Smith, Edell, Welter & Schmidt, P.A.
Claims
I claim:
1. A security access arrangement comprising:
a first part associated with an authorised person;
a second part adapted to be attached to an item; and
a third part associated with a restricted access area;
wherein the first, second and third parts include equivalent electronic
circuitry comprising:
a signal transmitting means adapted to transmit coded signals;
controller means in electrical connection with the signal transmitting
means and adapted to supply coded signals to the signal transmitting
means;
signal receiving means in electrical connection with the controller means
and adapted to receive coded signals and supply the received coded signals
to the controller means; and
a power supply adapted to power the operation of the signal transmitting
means, signal receiving means and controller means;
said first, second and third parts being separate from one another and
being arranged such that access to the restricted area can only be
obtained if the first, second and third parts are proximate one another.
2. The security access arrangement of claim 1 wherein said first and second
parts are arranged such that an alarm is activated by the controller means
if the controller means ceases to receive the coded signals from the
signal receiving means due to the separation of the parts being greater
than a pre-determined distance.
3. The security access arrangement as in claim 1 further including means
for indicating when the separation between the first part and the second
part exceed a pre-set range.
4. A security access arrangement including:
a signal enabling tag adapted to be carried by an authorised person and
adapted to transmit an enabling signal;
a signal transmitting tag adapted to transmit a coded transmit signal and
comprising signal enabling tag detection means adapted to detect the
presence of the signal enabling tag;
a signal receiver/controller means associated with an area of restricted
access and adapted to receive signals from the signal transmitting tag
when the signal transmitting tag is within a pre-set range and interpret
the received signals and to activate one or more predetermined functions;
said signal enabling tag, said signal transmitting tag and said signal
receiver/controller means all being separate from one another; and,
wherein the signal transmitting tag does not transmit the coded signal
unless the signal enabling tag and the signal transmitting tag are
proximate to one another.
5. The security access arrangement of claim 4 wherein the signal enabling
tag, signal transmitting tag, and receiver/controller means each have the
same electronic circuitry comprising:
a signal transmitting means adapted to transmit a coded signal which is the
enabling signal and coded transmit signal of the signal enabling tag and
signal transmitting tag respectively;
a controller means in electrical connection with the signal transmitting
means and adapted to supply coded signals to the signal transmitting
means;
signal receiving means in electrical connection with the controller means
and adapted to receive coded signals and supply the received coded signals
to the controller means; and,
a power supply adapted to power the operation of the signal transmitting
means, signal receiving means, and controller means.
6. The security access arrangement of claim 5 wherein the controller means
is a programmable microprocessor having a plurality of input lines and
output lines and includes associated memory means.
7. The security access arrangement of claim 5 wherein the controller means
is a programmable microprocessor having a plurality of input lines and
output lines and includes associated memory means and further comprising
one or more switches in electrical connection with the input lines of the
controller means, said switches being adapted to provide signals to the
controller means to enable one or more of a range of functions able to be
provided by the controller means.
8. The security access arrangement of claim 5 wherein either or both of the
signal enabling tag or the signal transmitting tag further comprises an
alarm which is activated by the controller means of the respective tag if
the separation between the signal enabling tag and the signal transmitting
tag exceeds a pre-determined distance so that the controller means of the
respective tag ceases to receive signals from the receiving means of the
respective tag.
9. The security access arrangement of claim 5 wherein the controller means
is adapted to perform one or more functions selected from the group
including: control all timing; generate code sequences; decode code
sequences; monitor switch operations; drive audible alerts; monitor power
supply voltage; and implement low power mode.
10. The security access arrangement of claim 5 wherein the signal
transmitting means transmits a low power, low duty cycle electromagnetic
signal which is amplitude modulated by a code sequence generated by the
controller means.
11. The security access arrangement of claim 5 wherein the signal receiving
means is adapted to receive and demodulate signals received from the
signal transmitting means.
12. The security access arrangement of claim 5 wherein the power supply
comprises a battery and solar power conversion means arranged such that
the solar power conversion means continuously charges the battery when the
solar power conversion means is exposed to ambient light.
13. The security access arrangement of claim 4 wherein the signal enabling
tag comprises a battery-free, radio frequency transponder that returns a
coded signal in response to an interrogating pulse from the signal
transmitting means of the signal transmitting tag.
14. The security access arrangement of claim 4 wherein the signal enabling
tag comprises a power supply and a radio frequency transmitter that
constantly transmits an identification coded signal.
15. The security access arrangement of claim 4 wherein the signal enabling
tag comprises a power supply, a radio frequency receiver/transmitter and
an encoder/decoder module.
16. The security access arrangement as in claim 4 further including means
for indicating when the separation between the signal enabling tag and the
signal transmitting tag exceed a pre-set range.
Description
This invention relates to a security access arrangement incorporating an
electronic key or electronic token, which automatically allows access to
an area by an authorised person based on the proximity of the key or token
to the area. In particular the invention provides a system that minimises
the risk of an unauthorised person gaining access to the area by
illegitimately obtaining a key or token.
BACKGROUND ART
Electronic key systems for accessing restricted areas are known and take a
number of forms. These include magnetic card readers, keypad door locks,
interrogator/transponder systems and various transmitter/receiver type
systems.
Magnetic card readers and keypad door locks offer minimal security or
convenience improvements compared to conventional mechanical locks. The
user must physically contact the card reader or keypad to obtain entry.
Both of these access control systems could easily be compromised by the
loss of the magnetic card or inadvertent disclosure of the keypad code. In
either case an unauthorised person could access the restricted area.
Interrogator/transponder systems and transmitter/receiver systems are more
sophisticated in that they do not require any physical action on the part
of the authorised person. These systems permit access based on the
proximity of a key or token to an access controller.
One early example of the interrogator/transponder security system is
described in U.S. Pat. No. 3,891,980 assigned to Lewis Security Systems
Ltd. This patent describes a system in which an authorised person carries
a token that generates signals at two discrete frequencies when the person
approaches a door leading to a restricted area. A sensor detects the
person's presence and activates a control unit which interrogates
inductive loops adjacent the door to determine if the correct signals are
being picked up. If the correct signals are present the door is opened
automatically, otherwise the door remains locked and an alarm may be
given.
The prior art includes many examples of transmitter/receiver security
systems designed primarily for automatic locking and unlocking of
automobile doors. Early devices required the user to push a button on a
transmitter that sent a radio frequency signal to a receiver to activate
solenoid-operated electronic door locks. More recent devices have removed
the necessity for any physical action by the user and work entirely on the
basis of proximity.
One such device is described in U.S. Pat. No. 4,688,036 assigned to Nissan
Motor KK. This patent describes a portable code signal transmitter that is
approximately the size and shape of a credit card. The transmitter
produces a radio frequency signal with a unique code that is detected by a
controller in a vehicle. Vehicle functions are actuated by the controller
when the unique code matches a preset code stored in the controller.
Another device is described in U.S. Pat. No. 4,942,393 assigned to Lectron
Products Inc. This patent describes a system to automatically unlock and
lock the doors of an automotive vehicle as a user approaches or moves away
from the vehicle. The system consists of a portable beacon carried by the
user, a receiver/controller in the vehicle and an antenna connected to the
receiver controller. The patent describes a number of improvements over
earlier devices including a motion sensor to conserve battery life and
transmitter signals embodying differential phase encoded data with error
correction coding of the data to enhance noise immunity and signal
discrimination.
The prior art patents have also addressed the problem of a user leaving the
transmitter in the vehicle, one example being U.S. Pat. No. 4,672,375. In
this patent the controller has many of the features described above but
also includes a disabler feature. The disabler becomes active when the
vehicle door is closed and locked, and disables the entry system if the
unique code is detected for a period exceeding a predetermined time. An
alarm sounds to remind the user to collect the transmitter.
The prior art sometimes refers to these systems as `keyless` referring to
the absence of conventional key and lock mechanisms although in the
strictest sense the mechanical key has merely been replaced by an
electronic key. The unique code transmitted by the electronic key is
analogous to the teeth pattern of a mechanical key. The electronic key can
be more versatile and the transmitted signal can provide functional
information as well as an identifying code. The ability to provide an
alarm if the electronic key is left in the vehicle is also a valuable
advantage.
Although having a number of advantages over conventional keys all the known
prior art devices suffer from the same problem of an unauthorised person
being able to access a restricted area (including a motor vehicle) by
simply gaining access to the signal generating device. Thus a device that
is lost, left or stolen can negate all of the security advantages embodied
in the "keyless" entry system.
This shortcoming is highlighted where such a system is embodied as a motor
vehicle security system. It is common for the signal generating device to
be embodied as a tag that is attached to a key ring holding the vehicle
keys. A carjacker can readily access a vehicle and operate the ignition if
they have the key ring with the tag attached. Prior art devices that
embody the signal generating device in the key head only exacerbate the
problem.
Clearly, an arrangement is needed which is disabled when separated from the
authorised person thereby preventing unauthorised persons from gaining
access to and use of the restricted area even if they hold a signal
generating device.
Devices to achieve this object exist in the form of retina pattern and
fingerprint recognition systems. While such devices would overcome the
stated problem they are too expensive and insufficiently portable to be a
practical solution to the problem of vehicle and facility security (except
in larger facilities). A more economically and practically viable solution
is required.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a security access
arrangement that operates when a security access device is proximate to an
authorised person but is disabled when the security access device is more
than a pre-set distance from the authorised person.
A further object of the present invention is to provide an arrangement that
alerts the authorised person when the security access device is removed by
greater than a pre-set distance from the authorised person.
It is a still further object of the invention to provide a number of
security access devices that can be individually configured for a
plurality of independent authorised persons to gain access to a restricted
area.
Another object of the present invention is to provide the public with an
economic and useful alternative to existing security access systems.
DISCLOSURE OF THE INVENTION
In one form of the invention although it need not be the only or indeed the
broadest form there is proposed a security arrangement comprising:
a first part associated with an authorised person;
a second part adapted to be attached to an item; and
a third part associated with a restricted access area;
wherein the first, second and third parts include equivalent electronic
circuitry comprising:
a signal transmitting means adapted to transmit coded signals;
controller means in electrical connection with the signal transmitting
means and adapted to supply coded signals to the signal transmitting
means;
signal receiving means in electrical connection with the controller means
and adapted to receive coded signals and supply the received coded signals
to the controller means; and
a power supply adapted to power the operation of the signal transmitting
means, signal receiving means and controller means;
said first, second and third parts being separate from one another and
being arranged such that access to the restricted area can only be
obtained if the first, second and third parts are proximate one another.
Although the parts may, include equivalent electronic circuitry each part
will preferably perform a separate function. The first part is a signal
enabling tag, the second part is a signal transmitting tag and the third
part is a signal receiver/controller.
Therefore, in a further form, the invention resides in a security access
arrangement including:
a signal enabling tag adapted to be carried by an authorised person and
adapted to transmit an enabling signal;
a signal transmitting tag adapted to transmit a coded transmit signal and
comprising signal enabling tag detection means adapted to detect the
presence of the signal enabling tag;
a signal receiver/controller means associated with an area of restricted
access and adapted to receive signals from the coded signal transmitting
tag when the signal transmitting tag is within a pre-set range and
interpret the decoded signals and to activate one or more predetermined
functions;
said signal transmitting tag and said signal receiver/controller means all
being separate from one another; and
wherein the signal transmitting tag does not transmit the coded transmit
signal unless the signal enabling tag and signal transmitting tag are
proximate to one another.
It will be appreciated that by requiring that the signal enabling tag and
the signal transmitting tag are proximate one another the loss or theft of
one or other of the tags does not result in compromise of the security
status of the restricted area. If the signal enabling tag is not within a
pre-set range of the signal transmitting tag the signal transmitting tag
will not transmit a coded signal and access to the restricted area cannot
be obtained.
The signal enabling tag may be embodied in an item that is normally located
on the authorised person. For example it may take the form of a belt
buckle, a ring, a pendant or a clip. If embodied as a clip it may be
attached to a valuable item such as a wallet, passport, mobile phone, etc.
The advantage of this arrangement will become evident as optional
additional features of the invention are explained.
The signal transmitting tag may be embodied in similar ways to prior art
devices such as on a key ring or as part of a conventional ignition key
(for vehicle applications). The signal transmitting tag should preferably
be unconstrained in its position whereas the signal enabling tag can be
constrained to a fixed location, such as a belt buckle.
In preference the signal enabling tag, signal transmitting tag and
receiver/controller each have the same electronic circuitry comprising:
a signal transmitting means adapted to transmit coded signals;
controller means in electrical connection with the transmitter means and
adapted to supply coded signals to the signal transmitting means;
signal receiving means in electrical connection with the controller means
and adapted to receive coded signals and supply the received coded signals
to the controller means; and
a power supply adapted to power the operation of the signal transmitting
means, signal receiving means and controller means.
In another form the signal enabling tag comprises a battery-free, radio
frequency transponder that returns a coded signal in response to an
interrogating pulse from the signal transmitting means. Low frequency,
short-range transponders using FM transmission techniques and suitable for
the present application are known. The coded signal transmitted by the
transponder is received by the signal enabling tag detection means which
then enables the coded signal transmitting means of the signal
transmitting tag.
In an alternative arrangement the signal enabling tag comprises a power
supply and a radio frequency transmitter that constantly transmits an
identification coded signal. This alternative requires periodic
replacement of the power source that could be indicated by a battery
charge indicator (visual or aural) at the signal enabling tag or signal
transmitting tag.
In a further alternative arrangement the signal enabling tag can comprise a
power supply, a radio frequency receiver/transmitter and an
encoder/decoder module. In this form the signal enabling tag would
transmit a unique code when polled by the transmitter of the signal
transmitting tag. The receiver of the signal enabling tag would need to be
constantly on to receive the polling signal but the transmitter would only
be activated as required. This alternative would have less power drain
than the preceding alternative but require more complex circuitry.
In preference the signal enabling tag detection means of the signal
transmitting tag includes a radio frequency receiver and the coded signal
transmitting means includes a radio frequency transmitter and the signal
transmitting tag further comprises a power supply, an encoder/decoder and
a controller.
In preference the signal transmitting tag further comprises a function
switch adapted to provide signals to the controller enabling one or more
of a range of functions able to be provided by the controller. The
controller is preferably a programmable microprocessor and may include
associated memory means.
In preference one or both of the signal transmitting tag and signal
enabling tag further include alarm means adapted to emit an alarm if the
distance between the tags exceeds a predetermined distance. Preferably an
alarm is also emitted to alert a low power supply condition.
In preference the receiver/controller comprises a power supply, a radio
frequency receiver, a decoder, a controller and code memory. The
controller is preferably a microprocessor adapted to compare decoded
signals from the decoder with stored signals from the code memory and to
output activating signals in response to the comparison.
In preference the power supplies are lithium batteries charged by solar
cells. The signal enabling tag and signal transmitting tag can operate
independent of the receiver/controller to provide an item security system
in which either or both tags emit an alarm if the separation between the
tags exceeds a predetermined amount. In the case where only one tag emits
an alarm it is preferable that the tag emitting the alarm is the one that
is in motion. This can be achieved by incorporating a motion sensor in the
tag.
Therefore, in a further form of the invention there is proposed an item
security arrangement comprising:
a signal enabling tag including enabling signal transmitting means; and
a signal transmitting tag including enabling signal detection means and
alarm means;
wherein the alarm means is adapted to provide an indication if the distance
between said tags exceeds a predetermined distance such that the enabling
signal is not detected by the enabling signal detection means.
In an alternative form both tags include enabling signal transmitting
means, enabling signal detection means and alarm means such that both tags
provide an alarm if the distance between said tags exceeds a predetermined
distance such that the enabling signal is not detected by the enabling
signal detection means.
BRIEF DESCRIPTION OF THE DRAWINGS
To further assist in understanding the invention reference will be made to
the following drawings in which:
FIG. 1 illustrates a typical embodiment of a security access arrangement;
FIG. 2 is a block diagram of the circuitry of the components of a security
access arrangement;
FIG. 3 is a block diagram of the circuitry associated with one embodiment
of the controller shown in FIG. 2;
FIG. 4 is a block diagram of the circuitry associated with one embodiment
of the transmitter shown in FIG. 2;
FIG. 5 is a block diagram of the circuitry associated with one embodiment
of the receiver shown in FIG. 2;
FIG. 6 is a block diagram of the circuitry associated with one embodiment
of the battery and solar cells shown in FIG. 2;
FIG. 7 is a timing diagram of the receiver and transmitter operations of a
security access arrangement;
FIG. 8 is a flowchart of the operation of the invention when configured as
a vehicle security access arrangement;
FIG. 9a is a block diagram of the circuitry of a first embodiment of a
signal enabling tag;
FIG. 9b is a block diagram of the circuitry of a second embodiment of a
signal enabling tag;
FIG. 9c is a block diagram of the circuitry of a third embodiment of a
signal enabling tag;
FIG. 10 is a block diagram of the circuitry of a signal transmitting tag;
FIG. 11 is a block diagram of the circuitry of a receiver/controller.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to the drawings in detail there is shown in FIG. 1 a sketch
of a typical manner of employing the security access arrangement of the
present invention. In the depicted application the invention is embodied
as a vehicle security arrangement. A person has a first part 1 attached to
a belt 4. A second part 2 is attached to a valuable item such as keys 5.
As long as the person has the keys, the first part 1 and the second part 2
will be in proximity to each other and access to the secure area, in this
case a vehicle, is possible.
Within the vehicle is a third part 3. The third part 3 receives signals
from the second part 2 which directs the third part 3 to perform certain
functions. These functions may be active, such as unlocking the doors, or
may be passive, such as enabling vehicle operation. The third part only
performs the functions if it detects a correct signal from the second part
which will only occur if the first part is in proximity.
It will be appreciated that each of the three parts of the security access
arrangement perform one or more of the functions of receiving,
transmitting and controlling. The electronic arrangement of each part may
be identical with only the required functions being activated. A block
diagram for the electronic arrangement of a part is shown in FIG. 2.
In one preferred embodiment, being the best method known to the inventor of
working the invention, each part comprises a controller 11 adapted to
receive signals from a receiver 13 and provide signals to a transmitter
12. The controller 11 may perform a variety of functions 15 and the
operation of the controller 11 may be adjusted by switches 14. The part is
powered by power supply 16. The preferred embodiments of each of these
elements are described in more detail below.
The preferred embodiment of the controller 11 and associated circuitry is
shown in FIG. 3. The inventor has found that a suitable component for the
controller is a PIC16C54 EPROM based 8 bit CMOS microcontroller available
from Microchip Technology Inc. The chip requires an operating voltage of
between 2.5 volts and 6.25 volts and is powered by 3 volts in the
preferred embodiment. I/O lines RA0 to RA3 are configured as input lines.
One of the inputs is configured to receive signals from the receiver 13
and two of the inputs are configured to receive signals from switches SW1
and SW2.
The switches may enable a number of operations such as remote vehicle
entry, silence the audible alarm or locate the other one of a pair of
parts.
I/O lines RB0 to RB7 are configured as outputs. Two of the lines are
configured to control the operation of the transmitter 12 and receiver 13.
The remainder of the lines are available for performing a variety of
functions 15. In the simplest situation the only function may be the
generation of an audible alarm such as by driving a piezoelectric disc. If
the controller is a component of the third part 3 the range of functions
will be more extensive and will include such functions as door locking or
unlocking.
The controller 11 performs a range of functions to control the operation of
the part including:
control all timing
generate code sequences
decode code sequences
monitor switch operations
drive audible alerts
monitor power supply voltage
implement low power mode.
FIG. 4 shows a schematic electric circuit for the preferred embodiment of
the transmitter 12. The transmitter is a low power device operating at 304
MHz. The transmitted signal is amplitude modulated by the code sequence
generated by the controller 11. To reduce power consumption and minimise
interference from other security access arrangements the transmitter is
operated with a low duty cycle. The signal is transmitted from L2 which is
formed as a PCB track.
A schematic electric circuit for the receiver 13 is shown in FIG. 5. The
receiver is tuned to receive signals at the same frequency as emitted by a
paired transmitter. The receiver demodulates the received amplitude
modulated signal and feeds the received code to the controller 11.
The preferred embodiment of the power supply 16 is depicted schematically
in FIG. 6. It comprises a battery B1 which is trickle charged by two solar
cell arrays SC1 and SC2. The battery is a 3 volt lithium cell that
provides all the power necessary for the component. The battery acts as an
accumulator by providing peak power requirements for the component and
recharging during period of low power requirement.
The two solar cell arrays generate the power for the component. Even under
moderately low light conditions, such as under incandescent lights, the
solar cells can generate sufficient power to operate the component.
As mentioned above the transmitter is operated at a low duty cycle to
conserve battery power. It is also desirable to only operate the receiver
when a transmitted signal is expected. An initial period is required for
the synchronisation of the transmitter and receiver of a pair of tags.
This is achieved by having the receiver continuously on until a signal is
received. Once a signal is received the controller locks to the
transmission duty cycle and only turns the receiver on accordingly. The
tags are preferably configured to operate on a peer-to-peer basis rather
than a master-slave basis so the transmitter and receiver duty cycles of a
pair of tags will be as depicted in FIG. 7.
Although each part of the security access arrangement can perform any role
it will be appreciated that in any given application each part will be
configured to perform a different role. To differentiate these roles and
assist in further description the first part associated with an authorised
person will be referred to as a signal enabling tag (SET), the second part
associated with an item will be referred to as a signal transmitting tag
(STT) and the third part associated with the restricted area will be
referred to as a receiver/controller.
To more fully explain the advantages of the invention the operation in a
specific application is described. FIG. 8 is a flowchart of the operation
of a security access system applied to an automotive vehicle.
The flowchart shows that the SET and STT check that a signal is present to
indicate that they are within a predetermined range. If the signals are
not present either or both tags emit alarms. If the STT is within range of
the vehicle and the SET is present the vehicle can be mobilised. If the
SET and STT are subsequently separated different actions occur depending
on the conditions. If the ignition is not on, the vehicle is immobilised
and the doors are locked. If the ignition is on but the vehicle is
stationary the ignition is turned off and the doors locked. If the
ignition is on and the vehicle is moving the vehicle is not immobilised
until the application of the brake pedal is applied and after a pre-set
time delay period has expired. This is to ensure that the ignition is only
turned off while the vehicle is slowing for reasons of safety.
If, for example, a vehicle user leaves the STT in the vehicle and ignores
the alarm the doors will lock automatically and the vehicle will be
immobilised. The user will still be able to access the vehicle because
when the user returns, the SET will be in range of the STT and the doors
can be automatically opened. A thief will not be able to steal the
vehicle, even though the keys are in the vehicle, because without the SET
the ignition will be inoperative.
Of course, any passenger in the vehicle will still be able to exit the
vehicle using the normal door handle, notwithstanding the automatic door
locking.
Other embodiments of the signal transmitting tag, signal enabling tag and
receiver/controller will be evident to persons skilled in the art of
electronics. A number of alternative arrangements are shown in the block
circuit diagrams of FIGS. 9, 10 and 11.
FIG. 10 shows a block circuit diagram for a signal transmitting tag (STT)
30 of a security access arrangement. The STT comprises a power supply 36,
a radio frequency transmitter/receiver 33, an encoder/decoder 32, a
controller 31, an alarm 35, and function switches 34. The embodiment of
FIG. 9 differs from the embodiment of FIG. 2 in that the encode/decode
function is shown separately from the controller. It will be appreciated
by those skilled in the art that this arrangement is functionally
equivalent to the first preferred embodiment.
FIGS. 9a, 9b and 9c show three alternative embodiments of the signal
enabling tag 20.
In one arrangement the radio frequency transmitter 33 periodically
transmits short interrogating pulses of radio frequency energy that are
received and retransmitted by a transponder 21 in a signal enabling tag
(SET) 20 as shown in FIG. 8a. The transponder retransmits a signal that
includes a code that is received by the STT receiver 33 and decoded by the
STT decoder/encoder 32. Provided the correct coded signal is received the
controller 31 enables the encoder 32 that passes a coded signal to the
transmitter 33 for transmission to the receiver/controller 40 (FIG. 11) to
facilitate access to the restricted facility.
If the STT receiver 33 does not receive a correctly encoded signal within a
few milliseconds (less than 100 msec) of the transmission of the
interrogating pulse the controller does not enable the encoder and access
to the restricted facility is not permitted. Furthermore, the controller
31 activates the alarm 35 to indicate that the SET is out of range thereby
warning the user to collect either the STT or SET from where it has been
left.
To reduce power supply use in the STT the restricted facility access signal
may only be transmitted on command. The command may be given by activating
function switch 34. Alternatively, a motion detector switch may be
employed or an enabling signal from the receiver/controller 40 may be
employed.
In another arrangement (FIG. 9b) the SET 20 comprises a power supply 22, an
encoder 23 and a radio frequency transmitter 24. In this embodiment the
transmitter 24 constantly or periodically transmits a coded signal that is
detected by the receiver 33 of the STT. As with the previous embodiment
the STT is only able to access the restricted facility if the signal from
the SET is received. If the SET signal is not received an alarm 35 is
activated as in the previous embodiment.
A further arrangement incorporates an alarm in both the STT and the SET.
The block circuit for the SET for this embodiment is shown in FIG. 9c. As
with the first arrangement the STT transmits an interrogating signal that
is received by the receiver/transmitter 26 and decoded by the
encoder/decoder 27. Providing the correct code is detected the
receiver/transmitter 26 transmits an encoded signal in response that is
received by the receiver 33 of the STT. If no interrogating signal is
received by the SET within a given time the alarm 28 is sounded.
Similarly, the alarm 35 will sound at the STT because a signal will not be
received from the SET.
The alarms may indicate either that the power supply of one or both of the
SET or STT is below a threshold level or that the SET and STT are not
within range of one another. Which of these situations apply will be
evident from the location of the SET and STT and remedial action can be
taken. Both the SET and STT may have alarm disable switches so that the
alarm can be turned off while the fault condition is corrected.
While a limited number of specific embodiments have been described it will
be evident to those skilled in the art that the various block circuits can
be employed in almost any combination. The best configuration in any given
situation will depend on the particular conditions and requirements.
Looking now at FIG. 11 there is shown an alternate arrangement for a
receiver/controller. The receiver/controller 40 comprises a power supply
41, radio frequency receiver 42, decoder 43, controller 44 and code memory
45. The receiver 42 receives a coded signal from the transmitter 33 of the
STT. The decoder 43 decodes the signal and passes the code to the
controller 44 where it is checked against a code memory 45. If the code is
an authorised code the controller performs the indicated function, such as
unlock doors, activate ignition etc.
It will be appreciated that the decoder 43, controller 44 and code memory
45 can be embodied in a single device such as the PIC16C54 device
described in the first preferred embodiment.
The controller 44 may also perform automatic functions such as relocking
doors if the STT moves out of range. In the case where the security access
system is used in an automotive vehicle application the controller 44 will
act to disable the vehicle in certain circumstances.
The code memory 45 stores the codes for all authorised users and all
functions. The function switch 34 of the STT can be configured to select
from a variety of functions and the appropriate code transmitted as
required. For example, a single depression of the function switch may
transmit a code to unlock vehicle doors, two quick depressions may
transmit a code to unlock doors and turn on the radio. Furthermore, the
code memory 45 can store individual codes for a large number of users.
Thus if one authorised user loses a tag the code for that tag can be
erased without affecting the integrity to all other tags.
In the preferred embodiments the controller 11, 31 or 44 is a
microprocessor programmed for the desired functions. The advantage of
using a microprocessor is that it can be programmed for any of a range of
desired functions and can be easily reprogrammed as required.
In a further preferred embodiment the invention can be employed as an item
security system wherein the SET is embodied in an item normally located on
an authorised person and the STT is attached to an item that it is desired
to secure. For this application of the invention both tags could have the
block circuit depicted in FIG. 2. Both tags would transmit a low power
coded signal to be received by the receiver of the other tag. If either
tag ceases to receive the signal it would sound an alarm. If only one
alarm sounds this would indicate a power supply problem. If the tags
become separated by greater than a predetermined amount both tags would
sound an alarm.
Throughout the description of preferred embodiments reference has been made
to low power transmitters and receivers which communicate over a limited
range. A break in communication due to exceeding the limited range results
in an alarm. The invention could also be configured to activate a higher
power transmission if the communication link is broken, the higher power
transmission would include a signal to activate the alarm. In some
situations a positive activation of the alarm may be preferable to a
negative activation (ie. loss of signal).
Other variations in the details of the embodiments of the invention will be
evident to those skilled in the art without departing from the spirit of
the invention.
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